WASHINGTON >> Congress, returning from summer break today, has a lot to get done in the next three weeks. At the top of its long to-do list: averting a government shutdown and casting the most significant foreign policy vote since the 2002 Iraq war authorization.

The legislative agenda is playing out against the backdrop of fresh doubts about the House speaker’s staying power. One conservative member says that a “sword of Damocles” hangs over John Boehner.

Expect intense floor debate on Iran, starting this week in the Senate. Sept. 17 is the deadline for action on an Iran nuclear agreement resolution. Democrats have the votes to allow the nuclear agreement to take effect. The question right now is whether President Obama can win the support of 41 senators, which would allow a filibuster of the planned Republican resolution of disapproval. That would spare him the need to use his veto pen.

Democrats have a hard whip count of 38 votes backing the Iran deal, meaning they only need three of these five: Connecticut’s Richard Blumenthal, Washington’s Maria Cantwell, Michigan’s Gary Peters, Oregon’s Ron Wyden and West Virginia’s Joe Manchin. Manchin complicated things a little when he said he won’t participate in an Iran filibuster, so his support would require another to come onboard.

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A continuing resolution must pass by Sept. 30 to keep the government from shutting down. It seems very unlikely there will be any agreement this month to lift the budget limits imposed by sequestration, even though there’s significant bipartisan support to do so. The reason is Republicans want to increase defense spending; Democrats say they’ll only go along if domestic program caps are lifted too, which many conservatives say would unacceptably grow the deficit. And, of course, most streams of fresh revenue are off the table.

So we’ll likely wind up with a short-term funding measure that once again kicks the can down the road. Republican sources say it’s unclear how long the extension will last, but it seems most likely that we’ll postpone a bigger spending showdown for later this year.

Planned Parenthood complicates the funding debate and makes real the possibility of an Oct. 1 shutdown. Undercover videos emboldened Ted Cruz and other conservatives to pledge they’ll oppose any spending bill, even something short-term, that includes money for the group. Democrats, including the White House, are adamant that they won’t cave and stress that federal law already prevents Planned Parenthood from using taxpayer money for abortions.

Republican leadership desperately wants to avoid a shutdown. They’re mindful of the lessons from the 2013 fight to defund Obamacare and this past winter’s failed gambit to defund the Homeland Security Department. Back home in Kentucky last week, Mitch McConnell reiterated that Republicans “just don’t have the votes” to defund Planned Parenthood.

That said, the base is angry enough that McConnell and Boehner may still need to engage in some degree of brinkmanship. From the right, the Senate majority leader faces 2016 GOP candidates — from Cruz to Marco Rubio, Rand Paul and Lindsey Graham — eager to impress social conservatives in the early states. From the center, McConnell must grapple with how to protect incumbent senators up for reelection next year in blue states who would seemingly want to avoid this battle as much as possible, such as Illinois’ Mark Kirk, Ohio’s Rob Portman or New Hampshire’s Kelly Ayotte.

Keep in mind there will be several days this month on which no legislating gets done: Rosh Hashanah is Sept. 14-15. Yom Kippur is Sept. 23. Pope Francis speaks to a joint session of Congress on Sept. 24, a day that will be full of fanfare and seems likely to become politicized.

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Boehner’s future as speaker in doubt. That’s the banner headline on Politico on Tuesday. “Figures in his close-knit circle of allies are starting to privately wonder whether he can survive an all-but-certain floor vote this fall to remain speaker of the House,” Jake Sherman and John Bresnahan report. “And, for the first time, many top aides and lawmakers in the House do not believe he will run for another term as House leader in 2017.” The reporters interviewed more than a dozen lawmakers and aides in direct contact with Boehner: “Uniformly they sympathized with his plight . . . But they also questioned Boehner’s viability in the near- and long-term.”

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The success of Donald Trump will embolden the right to challenge leadership more aggressively. “Mark Meadows looks like a much bigger deal than he did in July,” Post reporter Mike DeBonis reports Tuesday, looking at the unexpected challenge by the North Carolina congressman to Boehner just before recess. It does not currently have the votes to succeed, but the threat of a vote to oust Boehner — in which Democrats could meddle — will hang like a storm cloud over the remaining months of 2015.

Many, including Rep. Mick Mulvaney, R-S.C., now refer to the Meadows motion as a “sword of Damocles” hanging over Boehner. “If they haven’t gotten the message that they need to change the direction of our leadership, it could be a very ugly fall for our party,” said Mulvaney. “The people who are for Donald Trump are against John Boehner, and John needs to accept that and figure out what to do about it.”

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A new biography of Donald Trump comes out on Sept. 22 and The New York Times’ Michael Barbaro has an advance copy with some choice tidbits. In “Never Enough: Donald Trump and the Pursuit of Success,” by former Newsday reporter Michael D’Antonio, Trump, who never served in the military, says attending New York Military Academy gave him “more training militarily than a lot of the guys that go into the military.”

Perhaps the book’s juiciest nuggets come from interviews with The Donald’s ex-wives. Marla Maples remembers “the little boy that still wants attention.” And “Ivana Trump recalled sending 1/8Trump3/8 into a fit of rage by skiing past him on a hill in Aspen, Colo. Mr. Trump stopped, took off his skis and walked off the trail. ‘He could not take it, that I could do something better than he did,’ she said.” D’Antonio spent six hours interviewing the businessman but “the sessions abruptly ended, he writes, after Mr. Trump learned that Mr. D’Antonio had spoken with a longtime Trump enemy.” Trump tells the author he feels his essential temperament hasn’t changed since 1st grade.

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Hillary downplayed the email scandal in an interview with the AP in Cedar Rapids, saying it has not really affected her “very much.” Asked why she won’t directly apologize, Clinton said: “What I did was allowed. It was allowed by the State Department.” She added, “It is not a criminal investigation, it is a security review.” Asked for an example of how she differs with Bernie Sanders on policy, Clinton demurred. “I’m very much looking forward to the debates that we’re going to have and we’ll have plenty of time to draw those contrasts,” she said. Asked when she might start, Clinton said: “I don’t have any timing.”